Are IQ Tests reliable? Research Says They Are. Here's Why (2024)

Yes, IQ tests are definitely reliable. Indeed, reliability is a psychometric concept and can be calculated and quantified. All the most widely used IQ tests have a high proven degree of reliability and validity.

By “reliable” what the general public means is if the intelligence measurements produced by IQ tests are real or not.

Well, they are, and whether they are or not is something that can be studied and quantified psychometrically.

In psychometrics, an IQ test’s reliability represents the consistency of a test; to what extent a test is able to produce similar scores after each administration.

Think of it as a thermometer. If a thermometer indicated different amounts of kelvins each time it measured the temperature of something (assuming that the temperature of the object was not varying at all), then we would know that there is something wrong with it. We would know that the thermometer is broken.

Another thing people usually have in mind when they ask if IQ tests are reliable is whether these scores actually have something to do with intelligence, or whether they have something to do with life outcomes at all.

As we have discussed in other sections, IQ or general intelligence is a psychometric construct that has been proven to be reliable and valid, and it has shown to correlate with life outcomes that are of major importance for the individual, such as academic performance or professional and financial success, among others.

That takes us to the next important psychometric property all tests (and especially IQ tests) must have; validity.

In psychometry, validity refers to the extent to which a test or a tool measures what it is supposed to measure, or in this case, the extent to which it measures intelligence.

There are several ways to infer a test’s validity. For instance, it is possible to have test-takers take one test and then another one (aimed at measuring the same thing) that is already known to be valid. If the results of both tests have a significant correlation, then it means the newly created test is also valid.

Another way to infer the validity of a test is to find correlations between the results of the test and real-life outcomes. If these correlations are found, and these real-life outcomes are variables that fit within the definition of the construct being measured, that means the test is valid.

For instance, we would expect people who score high on IQ tests to exhibit results in a life that “intelligent” people are supposed to have. If, for instance, smarter people are better in the academic realm, then that means that those who score higher on a given IQ test should also be better academically. If they were not, if both variables turned out to be uncorrelated, then that would mean that there is something wrong with the IQ test under assessment.

So, in sum, IQ tests are both valid and reliable; they measure intelligence in a consistent way and the scores that they produce correlate with real-life outcomes, with those related to the construct of intelligence. Indeed, both statistics are assessed during the construction process of the IQ test.

Of course, that does not mean IQ tests are perfect and always produce perfect scores. That is false. Errors of measurement exist as well.

Smart people could be underscored and vice versa, depending on the conditions of the administration of the test or on the personality of the test-taker.

If the test-taker suffers from any sort of anxiety disorder, from stress, does not work well under pressure, or feels nervous during the test, he could get considerably lower scores than the ones he deserves.

In addition, this is not to say that absolutely everyone with a high IQ will be successful and absolutely everyone with an average IQ will not be successful. What we are pointing out is a trend, not an absolute. People with high IQs are more successful ON AVERAGE.

On what does the reliability of an IQ test depend?

How reliable an IQ test is depends on its property/capacity to produce measurements that are consistent (that are the same) across different observations of the same samples. That is what reliability means in psychometrics. Of course, these measurements are not error-exempt. Every measurement is thought to be subject to a certain degree of error, which is random, and too, quantifiable.

In general terms, the reliability of an IQ test will depend on its standard error of measurement (that is, the amount of measurement error it tends to produce in each observation) and on its reliability coefficient, which is the quantification of the reliability of a test, of the capacity to give similar measurements across different observations of the same samples.

The reliability coefficient of an IQ test can be calculated in several ways, but the most common one is to calculate it as the correlation between the scores of two administrations of the same test to the same sample at different points in time.

The standard error of measurement of an IQ test is calculated once the reliability coefficient is known, by using the following formula:

Where SEM stands for Standard Error of Measurement, S is the standard deviation of the measurements of our data, and rxx is the reliability coefficient.

Are online IQ tests reliable?

IQ tests are usually administered in person by a professional. Depending on the administration purposes of the test, administering it online might not be the best choice (eg: if it is going to be taken by a child or by someone with learning disabilities). However, in general, taking an IQ test online instead of doing so face-to-face with a professional should produce the same results. So yes, IQ tests administered online are generally reliable. Indeed, some valid, professional and widely-used IQ tests have online versions too (like the Raven’s progressive matrices from Pearsonas sessments), and their reliability is still pretty high.

However, if it is going to be completely self-administered, it should not be used with diagnostic purposes or to draw any definitive conclusions, nor to base any decisions on the results. In these cases, a professional should always have the last word, even if the test is administered online.

References:

https://www.researchgate.net/figure/Test-retest-reliability-data-gathered-from-34-separate-studies-on-common-IQ-tests-the_fig1_316640643

https://www.researchgate.net/publication/314856559_The_Predictive_Validity_of_Four_Intelligence_Tests_for_School_Grades_A_Small_Sample_Longitudinal_Study

https://www.verywellmind.com/what-is-reliability-2795786

https://www.researchgate.net/publication/222403422_Intelligence_and_Educational_Achievement

https://www.researchgate.net/publication/328416329_Intelligence_and_socioeconomic_success_A_study_of_correlations_causes_and_consequences

https://www.hrprofilingsolutions.com.au/blogs/aus-blog/measure-validity-psychometric-assessment/

https://pages.mtu.edu/~shanem/psy5220/daily/Day5/psychometrics.html

http://www.careergym.com/psychometric_glossary/standard_error_of_measurement_sem

https://en.wikipedia.org/wiki/Reliability_(statistics)

https://www.pearsonclinical.com.au/products/view/300

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